Hybrid switched mode/linear power amplifier power supply for use in polar transmitter

ABSTRACT

In one aspect this invention provides a DC-DC converter that has a switch mode part for coupling between a DC source and a load, the switch mode part providing x amount of output power; and that further has a linear mode part coupled in parallel with the switch mode part between the DC source and the load, the linear mode part providing y amount of output power, where x is preferably greater than y, and the ratio of x to y may be optimized for particular application constraints. In a further aspect there is a radio frequency (RF) transmitter (TX) for coupling to an antenna, where the TX has a polar architecture having an amplitude modulation (AM) path coupled to a power supply of a power amplifier (PA) and a phase modulation (PM) path coupled to an input of the PA, where the power supply includes the switch mode part for coupling between a battery and the PA and the linear mode part coupled in parallel with the switch mode part between the battery and the PA.

CLAIM OF PRIORITY FROM COPENDING PROVISIONAL PATENT APPLICATION

This patent application claims priority under 35 U.S.C. §119(e) fromProvisional Patent Application No.: 60/503,303, filed Sep. 16, 2003, thedisclosure of which is incorporated by reference herein in its entirety.

TECHNICAL FIELD

This invention relates generally to DC to DC converter power supplies,more specifically switched mode power supplies (SMPS) that are suitablefor use in radio frequency (RF) transmitters, such as RF transmittersfor cellular mobile stations that are embodied as envelope restoration(ER) RF transmitters, also known as polar transmitters, where a symbolis represented using phase and amplitude components, rather than complexIn-phase/Quadrature Phase (I/Q) components.

BACKGROUND

FIG. 1A is a simplified block diagram showing an ER transmitter (TX) 1architecture that includes an amplitude modulation (AM) chain and aphase modulation (PM) chain. Bits to be transmitted are input to a bitsto polar converter 2 that outputs an amplitude signal, via propagationdelay (PD) 3, to an amplitude modulator (AM) 4. The AM 4 (after digitalto analog conversion) supplies a signal for controlling the output levelof a TX power amplifier (PA) 6 through the use of a controllable powersupply 5. The bits to polar converter 2 also outputs a phase signal viapropagation delay 3 to a frequency modulator (FM) 7, which in turnoutputs a signal via a phase locked loop (PLL) 8 to the input of the PA6. The transmitted signal at an antenna 9 is thus generated bysimultaneously using both phase and amplitude components. The benefitsthat can be gained by using the ER transmitter architecture include asmaller size and an improved efficiency.

As can be appreciated, the supply voltage of the PA 6 should beamplitude modulated with high efficiency and with a wide bandwidth.

Discussing the power supply 5 and PA 6 now in further detail, highefficiency TX architectures, such as the polar loop modulation TX,typically rely on highly-efficient but non-linear power amplifiers, suchas switch mode power amplifiers (SMPA), for example a Class E SMPA, orthey rely on normally linear power amplifiers that are driven intosaturation, such as the saturated Class B power amplifier. In thesearchitectures the amplitude information is provided by modulating thesupply voltage of the PA 6 by means of a power regulator that isconnected between a DC supply or power source, typically a battery, andthe PA 6, as shown in greater detail in FIG. 1B.

In FIG. 1B the output of the power supply 5, V_(pa), should be capableof tracking a rapidly varying reference voltage V_(m). As such, thepower supply 5 must meet certain bandwidth specifications. The requiredbandwidth depends on the system in which the transmitter 1 is used. Forexample, the required bandwidth exceeds 1 MHz (dynamic range ˜17 dB fora given power level) for the EDGE system (8 PSK modulation), and exceeds15 MHz (dynamic range ˜47 dB for a given power level) for the WCDMA(wideband code division multiple access) system. As may be appreciated,these are very challenging requirements. A typical waveform (RF envelopein the EDGE system) that must be tracked is shown in FIG. 2, where themodulating voltage (V_(m)) is shown as varying between minimum and peakvalues (the typical rms and average values are also shown).

It is noted that in the GSM system the modulation is GMSK, which has aconstant RF envelope, and thus for a given power level imposes noparticular constraints in terms of bandwidth on the power supply 5.

In general, there are two primary techniques to implement the powersupply 5. A first technique, shown in FIG. 3, uses a linear regulatorimplemented with a summing junction 10, a driver 12 and a power device14. While a high bandwidth can be obtained, the efficiency is low due tothe voltage drop (V_(drop)) across the power device 14.

A second technique, shown in FIG. 4, would be to use a switch moderegulator. In this technique, which is not admitted has been previouslyused in a polar or ER transmitter, a step-down switching regulator 16would include a Buck-type or similar converter 18 and voltage-modecontrol circuitry 20. The PA 6 is shown represented by its equivalentresistance R_(pa). While the efficiency of the switch mode regulator 16can be very high, the required bandwidth would be difficult orimpossible to obtain. More specifically, if one where to attempt the useof the switching regulator 16 it would require a very high switchingfrequency (e.g., at least approximately five times the requiredbandwidth, or 5–10 MHz or more for EDGE and over 80 MHz for WCDMA).While a switching frequency of 5–10 MHz would be very technicallychallenging (typical commercial DC-DC converters operate with maximumswitching frequencies in the range of about 1–2 MHz), a DC-DC converterhaving a 100 MHz switching frequency, for example, is currentlyimpractical to implement, especially in low cost, mass produced devicessuch as cellular telephones and personal communications terminals.

In U.S. Pat. No. 6,377,784 B2, “High-Efficiency Modulation RFAmplifier”, by Earl McCune (Tropian, Inc.), there is purportedlydescribed high-efficiency power control of a high-efficiency (e.g.,hard-limiting or switch-mode) power amplifier in such a manner as toachieve a desired modulation. In one embodiment, the spread between amaximum frequency of the desired modulation and the operating frequencyof a switch-mode DC-DC converter is purportedly reduced by following theswitch-mode converter with an active linear regulator. The linearregulator is said to be designed so as to control the operating voltageof the power amplifier with sufficient bandwidth to faithfully reproducethe desired amplitude modulation waveform. The linear regulator is saidto be further designed to reject variations on its input voltage evenwhile the output voltage is changed in response to an applied controlsignal. The rejection is said to occur even though the variations on theinput voltage are of commensurate, or even lower, frequency than that ofthe controlled output variation. Amplitude modulation is said may beachieved by directly or effectively varying the operating voltage on thepower amplifier while simultaneously achieving high efficiency in theconversion of primary DC power to the amplitude modulated output signal.High efficiency is purportedly enhanced by allowing the switch-modeDC-to-DC converter to also vary its output voltage such that the voltagedrop across the linear regulator is kept at a low and relativelyconstant level. It is said that time-division multiple access (TDMA)bursting capability may be combined with efficient amplitude modulation,with control of these functions being combined, and that the variationof average output power level in accordance with commands from acommunications system may also be combined within the same structure.

SUMMARY OF THE PREFERRED EMBODIMENTS

The foregoing and other problems are overcome, and other advantages arerealized, in accordance with the presently preferred embodiments ofthese teachings.

In one aspect this invention provides a DC-DC converter that has aswitch mode part for coupling between a DC source and a load, the switchmode part providing x amount of output power; and that further has alinear mode part coupled in parallel with the switch mode part betweenthe DC source and the load, the linear mode part providing y amount ofoutput power. In the preferred embodiment x is preferably greater thany, and the ratio of x to y may be optimized for particular applicationconstraints. Further, the linear mode part exhibits a faster responsetime to a required change in output voltage than the switch mode part.In one embodiment the linear mode part includes at least one poweroperational amplifier operating as a variable voltage source, while inanother embodiment the linear mode part includes at least one poweroperational transconductance amplifier operating as a variable currentsource.

In a further aspect this invention provides a RF transmitter (TX) forcoupling to an antenna. The TX has a polar architecture and includes anamplitude modulation (AM) path coupled to a power supply of a poweramplifier (PA), and a phase modulation (PM) path coupled to an input ofthe PA. The power supply is constructed so as to have a switch mode partfor coupling between a battery and the PA, the switch mode partproviding x amount of output power, and to further have a linear modepart coupled in parallel with the switch mode part between the batteryand the PA. The linear mode part provides y amount of output power,where x is preferably greater than y, and the ratio of x to y may beoptimized for particular application constraints. Preferably the linearmode part exhibits a faster response time to a required change in outputvoltage than the switch mode part.

In a still further aspect this invention provides a method to operate aRF TX having the polar architecture comprised of the AM path that iscoupled to the power supply of the PA and the PM path that is coupled tothe input of the PA, the method including providing the power supply soas to comprise a switch mode part for coupling between a power sourceand the PA, the switch mode part providing x amount of output power; andcoupling a linear mode part in parallel with the switch mode partbetween the power source and the PA, the linear mode part providing yamount of output power, where x is preferably greater than y, and theratio of x to y may be optimized for particular application constraints,and where the linear mode part exhibits a faster response time to arequired change in output voltage than the switch mode part.

In operation, the power supply provides higher power conversionefficiency than a purely linear voltage regulator-based power supplywhile also providing a wider operational bandwidth than a purely switchmode-based power supply.

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing and other aspects of these teachings are made more evidentin the following Detailed Description of the Preferred Embodiments, whenread in conjunction with the attached Drawing Figures, wherein:

FIG. 1A is a block diagram of a conventional ER RF transmitter;

FIG. 1B is a block diagram of a conventional SMPA supplied with anamplitude modulated voltage by a power supply;

FIG. 2 is a waveform diagram showing a typical example of a referencevoltage V_(m) that must be tracked by the power supply of FIGS. 1A and1B;

FIGS. 3A and 3B show conventional examples of a linear voltage regulatorsupplying the PA;

FIGS. 4A and 4B show examples of a switching regulator supplying the PA;

FIG. 5 is a block diagram of the PA supplied by a hybrid voltageregulator in accordance with this invention, where a linear part of thehybrid voltage regulator preferably processes only a small part of therequired output power, and provides the necessary bandwidth, while aswitch mode part preferably supplies the majority of the output powerwith high efficiency;

FIGS. 6A–6F illustrate simplified schematic diagrams of embodiments ofthe hybrid voltage regulator shown in FIG. 5;

FIGS. 7A and 7B, collectively referred to as FIG. 7, relate to thecircuit shown in FIG. 6A, where FIG. 7A illustrates the general circuitconcept and where FIG. 7B shows the switching part in more detail;

FIG. 8 shows waveforms that correspond to the operation of the circuitof FIG. 7;

FIG. 9 also shows waveforms that correspond to the operation of thecircuit of FIG. 7;

FIGS. 10A and 10B, collectively referred to as FIG. 10, relate to thecircuit shown in FIG. 6B, where FIG. 10A illustrates the general circuitconcept and where FIG. 10B shows the switching part in more detail;

FIG. 11 shows waveforms that correspond to the operation of the circuitof FIG. 10;

FIG. 12 also shows waveforms that correspond to the operation of thecircuit of FIG. 10;

FIGS. 13A and 13B, collectively referred to as FIG. 13, relate to thecircuits shown in FIGS. 6C and 6D, where FIG. 13A illustrates thegeneral circuit concept and where FIG. 13B shows the switching part inmore detail;

FIG. 14 shows waveforms that correspond to the operation of the circuitof FIG. 13;

FIG. 15 also shows waveforms that correspond to the operation of thecircuit of FIG. 13;

FIGS. 16A and 16B, collectively referred to as FIG. 16, relate to thecircuits shown in FIGS. 6E and 6F, where FIG. 16A illustrates thegeneral circuit concept and where FIG. 16B shows the switching part inmore detail;

FIG. 17 shows waveforms that correspond to the operation of the circuitof FIG. 16;

FIG. 18 also shows waveforms that correspond to the operation of thecircuit of FIG. 16;

FIGS. 19A and 19B, collectively referred to as FIG. 19, show anequivalent circuit diagram of a Voltage Controlled Voltage Source (VCVS)and a VCVS circuit embodied as a Power Operational Amplifier (POA),respectively;

FIGS. 20A and 20B, collectively referred to as FIG. 20, show anequivalent circuit diagram of a Voltage Controlled Current Source (VCCS)and a VCCS circuit embodied as an Operational Transconductance Amplifier(OTA), respectively;

FIG. 21 illustrates a first control configuration wherein both theswitching part and the linear part are operated closed-loop and have asa reference a modulating signal V_(m);

FIG. 22 illustrates a second control configuration wherein both theswitching part and the linear part are operated closed-loop, where thelinear part has as a reference the modulating signal V_(m) and theswitching part has as reference the output of the linear part;

FIG. 23 illustrates a third control configuration wherein only thelinear part operates closed-loop and has as a reference the modulatingsignal V_(m), and where the switching part operates open-loop, and onlythe modulating signal V_(m) information is used to generate the dutycycle of the switching part;

FIG. 24 shows, further in accordance with embodiments of this invention,the parallel connection of a switching regulator and a linear regulatorvia an auxiliary inductor L₁ and an (optional) auxiliary capacitor C₁;

FIGS. 25A and 25B, collectively referred to as FIG. 25, show a controlblock diagram in accordance with the embodiment shown in FIG. 24, wherein FIG. 25A both the switching regulator and the linear regulator aremasters, and in FIG. 25B the linear regulator is the master and theswitching regulator is the slave;

FIGS. 26A and 26B, collectively referred to as FIG. 26, show a firstmulti-mode (multi-PA) control block diagram in accordance with theembodiment shown in FIG. 24, where all PAs are connected on the samesupply line at the output of the linear regulator, and where in FIG. 26Aboth the switching regulator and the linear regulator are masters, andin FIG. 26B the linear regulator is the master and the switchingregulator is the slave;

FIGS. 27A and 27B, collectively referred to as FIG. 27, show a secondmulti-mode control block diagram in accordance with the embodiment shownin FIG. 24, where a GSM/EDGE PA is connected at the output of theswitching regulator and a WCDMA PA is connected at the output of thelinear regulator, where in FIG. 27A both the switching regulator and thelinear regulator are masters, and in FIG. 27B the linear regulator isthe master and the switching regulator is the slave (in the WCDMA modeonly);

FIG. 28 illustrates a SMPA as (a) a block representation, (b) modeled byits equivalent DC resistance R_(pa), and (c) modeled by its equivalentDC resistance R_(pa) in parallel with capacitance C_(pa) used to achievePA stability;

FIGS. 29A and 29B, collectively referred to as FIG. 29, show a thirdmulti-mode control block diagram in accordance with the embodiment shownin FIG. 24, where a GSM/EDGE PA and a WCDMA PA are each connected toindependent supply lines associated with two linear regulators, where inFIG. 29A the switching regulator and each of the linear regulators aremasters, and in FIG. 29B the linear regulators are each a master and theswitching regulator is the slave (in the WCDMA mode only); and

FIGS. 30A and 30B, collectively referred to as FIG. 30, show a fourthmulti-mode control block diagram in accordance with the embodiment shownin FIG. 24, where a GSM/EDGE PA is connected to the output of theswitching regulator, where a WCDMA PA and a CDMA PA are each connectedto independent supply lines associated with two linear regulators, wherein FIG. 30A the switching regulator and each of the linear regulatorsare masters, and in FIG. 30B the linear regulators are each a master andthe switching regulator is the slave (in the WCDMA and CDMA modes only).

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring to FIG. 5, this invention provides a hybrid voltage regulatoror power supply 30 that combines a switching part 32, that processespreferably the majority of the power with high efficiency but lowbandwidth, with a linear part 34, that preferably processes a smallerpart of the required power with less efficiency but with high bandwidth.The result is a power supply that has the required bandwidth and anefficiency somewhat lower than that of a purely switching power supply,but still significantly higher than that of the purely linear regulator.The resulting hybrid power supply 30 provides an improved output voltagequality, as the linear part 34 can be used to compensate the outputvoltage ripple that is normally associated with a purely switching modepower supply. This is a significant benefit, as an excessive amount ofoutput voltage ripple can adversely affect the output spectrum of the PA6.

It is noted that in principle the amount of power (x) that is processedby the switching part 32 is greater than the amount of power (y)processed by the linear part 34. This is generally a desirable situationand, in fact, in many embodiments x is much greater than y. However,this relationship between the power processed by the switching part 32and the linear part 34 is not to be construed as a limitation of thepreferred embodiments of this invention. In principle, one desires tomaximize the ratio of x to the total power: the larger is this ratio,the higher is the efficiency. However, the actual ratio that is realizedin a given application can be a function of one or more of the followingfactors and considerations:

(a) the intended application (RF system specifics, such as the spectrumof RF envelope, amplitude of high frequency AC components, etc); and

(b) the implementation, where one may decide to some extent how muchpower to process with the switching part 32 and how much with the linearpart 34. For example, in EDGE one can process almost all of the powerwith the switching part 32 by using a 6–7 MHz switching frequency, orless power by using a slower switching converter operating at, e.g., 1MHz. One may also in certain situations, e.g., at very low power,disable the switching part 32 and use only the linear part 34, in whichcase the relationship x>y does not apply at all.

(c) Also to be considered may be trade-offs in efficiency vs.implementation complexity, as it is generally simpler to realize a slowswitching converter, but then the efficiency is reduced because a largerportion of the power needs to be processed by linear part 34.

(d) Also to be considered may be trade-offs intended to optimize theoverall efficiency. For example, a switching part 32 with very highswitching frequency and high bandwidth may process most of the power ina given application (x much larger than y), but the processing in theswitching part 32 may be with low efficiency due to the very highswitching frequency. Therefore it may be more advantageous to attempt tooptimize the overall efficiency through a trade-off between using alower switching frequency for better efficiency in the switching part32, versus a lower amount of energy processed in the switching part 32.

Thus, in general the portion of the power x processed by the switchingpart 32 is preferably greater than the portion of the power y processedby the linear part 34, and also the ratio of x to y is preferablyoptimized for the constraints imposed by a given application, andpossibly also by a particular mode of operation (e.g., in the low powermode mentioned above, where all power may be processed by the linearpart 34). A combination may also be considered, such that x ispreferably greater than y, and the ratio of x to y also may be optimizedfor the application constraints.

In practice, the invention may be implemented by taking a portion of thetopology of a switching converter (referred to in FIG. 5 as the“switching part”) and paralleling it with a voltage or a current source(referred to in FIG. 5 as the “linear part”). The output capacitor (C)of the Buck (step-down) converter 18 of FIG. 4A is removed. In the Buckconverter 18 the capacitor acts as a voltage source to maintain theoutput voltage constant. When the voltage at the output is required tobe increased, a large current must be provided via the inductor (L) tomeet the increased demand of the load and to charge the capacitor (C) tothe new, higher voltage level. This operation makes the switchingregulator 16 slow, and limits the bandwidth. However, if the capacitor(C) is replaced by a voltage source, the increased (or decreased)voltage level can provide very quickly via the paralleled voltage sourceof the linear part 34, while the slower switching part readjusts itsoperating point.

Referring again also to FIG. 2, the switching part 32 provides theaverage level V_(m) _(—) _(av), while the linear part 34 provides the ACcomponent superimposed on the average level.

An alternative embodiment, based on the same concept, uses a currentsource in place of the voltage source in the linear part 34.

The voltage source of the linear part 34 may be implemented using apower operational amplifier (POA), while the current source of thelinear part 34 may be implemented using a power operationaltransconductance amplifier (OTA). The operational amplifier of thelinear part 34 can be supplied by the battery voltage (V_(bat)) as shownin FIG. 5. In an alternative, presently more preferred embodiment (froman efficiency point of view) the operational amplifier of the linearpart 34 is supplied with the voltage V_(m) _(—) _(pk) from FIG. 2, i.e.,with a voltage that corresponds to the amplitude of the referencesignal, where V_(m) _(—) _(pk) is always lower than V_(bat). Inpractice, it is preferred to supply the operational amplifier of thelinear part 34 with the voltage V_(m) _(—) _(pk) plus some margin (0.2Vfor example) that is need to obtain correct operation of the linearstage.

FIGS. 6A–6F illustrate various embodiments of the hybrid voltageregulator 30 shown in FIG. 5, where FIGS. 6A, 6C and 6D show the use ofa variable voltage source 34A (e.g., the power operational amplifiermentioned above), and where FIGS. 6B, 6E and 6F show the use of avariable current source 34B (e.g., the power operationaltransconductance amplifier mentioned above). Note that in FIG. 6C twovariable voltage sources 34A and 34A′ are used, and that in FIG. 6D thetwo variable voltage sources 34A and 34A′ are capacitively coupled viaC1 to the output power rail of the switching part 32. Note as well thatin FIG. 6E two variable current sources 34B and 34B′ are used, and thatin FIG. 6F the two variable current sources 34B and 34B′ arecapacitively coupled via C1 to the output power rail of the switchingpart 32.

Based on the foregoing description it can be appreciated that the use ofthis invention allows the realization of an efficient PA power supply 30for TX architectures where the PA supply voltage is required to beamplitude modulated. Currently, this is possible only by using theinefficient linear regulator (see FIGS. 3A and 3B), as there is noswitching regulator commercially available, that is known to theinventor, that would provide the required bandwidth.

The foregoing and other embodiments of this invention are now describedin even further detail.

The circuit shown in FIG. 7 relates to the circuits shown in FIG. 6A,where FIG. 7A illustrates the general circuit concept and where FIG. 7Bshows the switching part 32 in more detail. The switching part 32 isobtained from a Buck converter, which is a step-down switching DC-DCconverter composed of two switching devices and an L-C filter. Theswitching devices, represented in FIG. 7B as complementary MOStransistors (PMOS/NMOS), conduct alternatively with duty-cycle d (d=theratio of time t_(on) _(—) _(PMOS), when the upper switch is conducting,to the switching period T_(s)). The control signal with duty-cycle d canbe obtained from an analog Pulse Width Modulator (PWM) block 32A, whichconverts a control voltage V_(ctr) _(—) _(sw) to a PWM signal with dutycycle d by comparing V_(ctrl) _(—) _(sw) with a sawtooth signal havingperiod T_(s). The PWM signal, fed to transistor driver stage 32B, canalso be generated with other methods, such as in a digital PWM block.

The conventional Buck converter typically includes an L-C output filter,where C is large enough so that the characteristic of the Buck converteris that of a voltage source. However, in the presently preferredembodiments of this invention the filtering capacitor is removed, or isretained but with minimal capacitance. As such, block 32 is referred toherein as a “switching part”, as opposed to a “switching converter”. Inpractice, a physical circuit will have some filtering capacitance, forexample, an amount needed to ensure the stability of the RF PA 6.However, it is assumed for the purposes of this invention that thecapacitance value (C) is significantly less than that found in aconventional Buck converter, so that the characteristic of the switchingpart 32 is predominantly that of a current source, and not a voltagesource.

More specifically, the switching part 32 has the characteristic of acurrent source due to the inductor (L) (and no/minimal capacitance C),but is not an actual Voltage Controlled Current Source (VCCS). Anincrease in the control voltage V_(ctrl) _(—) _(sw) determines anincrease in the duty-cycle d, which determines an increase in averageoutput voltage V_(pa), which in turn determines an increase in PA 6current I_(pa), and hence an increase in the DC component of theinductor current I_(L). However, the absolute value of the PA 6 currentI_(pa) is determined not solely by the control voltage V_(ctrl) _(—)_(sw) but also by R_(pa), as I_(pa)=V_(pa)/R_(pa). Thus, while thistechnique may resemble operation of a “VCCS”, it does not directlycontrol the current and is therefore referred to as being “VCCS-like”.

The linear part 34 functions as a Voltage Controlled Voltage Source(VCVS) 34A, and its output voltage V_(o) is controlled by thedifferential voltage V_(d), with differential amplification A_(d).

More specifically, FIG. 7A illustrates this embodiment of the inventionby assuming ideal sources: where the switching part 32 behaves like acurrent source and is connected in parallel with the linear part 34 thatbehaves like a bi-directional (i.e., it can both source and sinkcurrent) Voltage Controlled Voltage Source 34A. The linear part 34,being a voltage source, sets the PA 6 voltage V_(pa). The current i_(sw)from the switching part 32 adds with the current i_(lin) from the linearpart 34 to form the PA 6 current i_(pa) (R_(pa) represents the effectiveresistive impedance of the PA 6). The optional DC-blocking decouplingcapacitor C_(d) may be connected to ensure that the linear part 34contributes only the AC component.

FIG. 7B shows that the switching part 32 is implemented with thestep-down Buck converter from which the output filtering capacitance Chas been eliminated or reduced significantly. The current i_(sw) fromthe switching part 32 is thus in practice the inductor current i_(L),resulting in essentially current-source-like behavior (the inductor Lcan be assimilated to a current source).

It is instructive to note that since the linear part 34 has thecharacteristics of a voltage source, it can fix the voltage level V_(pa)applied on the PA, and that there is a means to control this voltagelevel. In addition, the linear part 34 is fast (wide bandwidth), henceit is possible to provide fast modulation of V_(pa). Note further thatthe VCVS 34A of the linear part 34 is bidirectional, in the sense thatcan both source and sink current.

As shown in FIG. 19B, the VCVS 34A can be implemented as a PowerOperational Amplifier (POA). The POA includes an operational amplifier(OPAMP) with a class A(B) stage that is able to sink/source the requiredcurrent. FIG. 19B shows a Class B power stage comprised of transistorsQ₁ and Q₂, but variations in the output stage design are possible toimprove performance. For example, in practice the power stage could beimplemented as a Class AB stage to reduce crossover distortion.

As was noted, the optional decoupling capacitor C_(d) may be introducedto ensure that the linear part 34 provides only the AC currentcomponent. However, there are certain situations wherein it would beadvantageous to allow the linear part 34 to also provide the DCcomponent, albeit with more complicated control. As one example, it maybe desirable to provide the DC component from the linear part 34 at lowpower levels where the switching part 32 maybe de-activated and wherethe PA 6 current would be provided only by the linear part 34. Asanother example, it may be desirable to provide the DC component fromthe linear part 34 at low battery voltage levels, e.g. 2.9V, when theV_(pa) _(—) _(peak) is very close to this value, e.g. 2.7V, and theswitching part 32 is not able to provide it. In such cases the optionalC_(d) would be removed.

The operation of the circuit shown in FIG. 7A is illustrated with thesimulated waveforms shown in FIG. 8, and the operation of circuit shownin FIG. 7B is illustrated with the simulated waveforms shown in FIG. 9.

The top waveform in FIG. 8 shows the resulting PA 6 voltage V_(pa). ThePA 6 voltage V_(pa) is set by the linear stage 34 having the voltagesource characteristic. In this example V_(pa) has a DC component (2V)plus an AC component shown as a 15 MHz voltage sine wave representingfast modulation. The second waveform from the top shows the currentcontribution of the switching part 32, the constant current i_(sw). Thethird waveform from top shows the current contribution of the linearpart, the AC component i_(lin) (a 15 MHz sine wave). As was noted, thelinear part 34 functions as a bi-directional voltage source, i.e., itcan both source and sink current. The bottom waveform shows that theresulting PA 6 current i_(pa) has both a DC component from the switchingpart 32 and an AC component from the linear part 34.

Note that in FIG. 8 one set of waveforms is for a sine wave of amplitudezero (no contribution form the linear part 34, designated with “A”), andthe other for a sine wave of non-zero amplitude (to show thecontribution from the linear stage, designated with “B”). This sameconvention is used in the waveform diagrams of FIGS. 9, 11, 12, 14, 15,17 and 18.

FIG. 9 depicts simulated waveforms to illustrate the operation of thecircuit shown in FIG. 7B. It is assumed for this non-limiting examplethat the switching stage 32 has a switching frequency of 5 MHz and aduty cycle of 0.5. The top waveform shows the PWM 32A voltage applied onthe inductor L at node pwm. Second waveform from the top shows theresulting PA 6 voltage V_(pa). The PA 6 voltage V_(pa) is set by thelinear stage 34 having the voltage source characteristic. In thisexample V_(pa) has a DC component (2V) plus an AC component of 15 MHz(voltage sine wave) representing the fast modulation. The third waveformfrom the top depicts the current contribution of the switching part 32,i.e., the inductor current i_(L)=i_(sw). In this case the current is notconstant, as in the ideal case depicted in FIG. 8, but has the specifictriangular shape encountered in switching converters. The switching part32 contributes a DC component and a triangular AC component (theinductor current ripple). The fourth waveform from top shows the currentcontribution of the linear part 34, the AC component i_(lin) (15 MHzsine wave plus inductor current ripple compensation). Note that thelinear part 34 contributes not only the 15 MHz sinusoidal component, butalso an AC component to compensate for the inductor current ripple (asseen clearly from the underlying waveform designated AC_(rip)). This isdue to the voltage source characteristic of the linear part 34 which,being a bi-directional voltage source, can both source and sink current.The bottom waveform shows that the resulting PA 6 current i_(pa) has aDC component from the switching part 32 and an AC component from thelinear part 34, where the AC triangular component of the inductorcurrent (third trace) is compensated by the linear stage 34.

FIG. 10 shows an embodiment where a Voltage Controlled Current Source(VCCS) 34B is used to construct the linear part 34. In general, the sameconsiderations apply as in the embodiment of FIG. 7, the onlysignificant difference being that the VCCS is not capable itself to fixthe PA 6 voltage level. Instead, the PA 6 voltage is determined by thetotal current injected into R_(pa). The implementation of the linearpart 34 can be as an Operational Transconductance Amplifier (OTA), asdepicted in FIG. 20B. In this simplified view the collector current ofQ₁ (Ic₁) in the differential pair is mirrored as I₅, while the collectorcurrent of Q₂ (Ic₂) is mirrored as I₃ and then I₄. The output current isI₀=I₅−I₄, and is proportional to the difference between the collectorcurrents IC₁–IC₂, which in turn is proportional to the differentialvoltage V_(d). As was noted, FIG. 20B shows a simplified representationof the OTA. In practice, a circuit implementation would aim to optimizethe accuracy of the current mirrors and to obtain a linearcharacteristic I₀=gV_(d).

The operation of the circuit shown in FIG. 10A is illustrated with thesimulated waveforms of FIG. 11, while the operation of the circuit shownin FIG. 10B is illustrated with the simulated waveforms of FIG. 12.

In FIG. 11 the top waveform shows the resulting PA 6 voltage V_(pa). Itis assumed that, from the power supply point of view, the PA 6 behaveslike a resistive load. Therefore V_(pa)=R_(pa)(i_(sw)+i_(lin)), i.e.,the PA 6 voltage is set by the sum of the currents supplied by theswitching part 32 and the linear part 34. In this example, R_(pa) isassumed to equal two Ohms. The switching part 32 contributes the DCcomponent i_(sw) (e.g., 1 Amp) and the linear part 34 contributes the ACcomponent i_(lin), a 15 MHz current sine wave representing the fastmodulation. The second waveform from the top shows the currentcontribution of the switching part 32, i.e., the 1 Amp constant currenti_(sw). The third waveform from the top depicts the current contributionof the linear part 34, that is, the AC component i_(lin) (the 15 MHzcurrent sine wave). The bottom waveform shows that the resulting PA 6current i_(pa) has a DC component from the switching part 32 and an ACcomponent from the linear part 34.

In FIG. 12 it is assumed that the switching stage 32 has a switchingfrequency=5 MHz and duty cycle=0.5. The top waveform shows the PWM 32Avoltage applied on the inductor L at node pwm. The second waveform fromthe top shows the resulting PA 6 voltage V_(pa). As was noted above, itis assumed that the PA 6 behaves like a resistive load and, therefore,V_(pa)=R_(pa)(i_(sw)+i_(lin)), i.e., the PA 6 voltage is set by the sumof the currents supplied by the switching part 32 and the linear part34. As before, R_(pa) is assumed to equal two Ohms. The switching partcontributes the DC component i_(sw) (1 Amp) having a triangular ACcomponent. The linear part contributes the AC component i_(lin), such asthe 15 MHz current sine wave representing the fast modulation. The thirdwaveform from top shows the current contribution of the switching part32, i.e., the inductor current i_(L)=i_(sw). In this case the current isnot constant, as in the ideal case depicted in FIG. 11, but has thetriangular shape encountered in switching converters. The switching part32 contributes the DC component and the triangular AC component (theinductor current ripple). The fourth waveform from top shows the currentcontribution of the linear part 34, i.e., the AC component i_(lin) (15MHz sinusoidal component). Note that in this case the linear part 34contributes only the 15 MHz sinusoidal component, unlike thecorresponding waveform from FIG. 9, where the AC component to compensatefor the inductor current ripple can also be seen. The bottom waveformshows that the resulting PA 6 current i_(pa) has the DC component andthe AC triangular component from the switching part 32 (as seen from theunderlying waveform designated ACrip), and the AC component from thelinear part 34. Note that the AC triangular component is not compensatedfor by the linear stage 34 in this embodiment due to its current sourcecharacteristic, although it may be compensated by suitably controllingthe VCCS.

The circuits shown in FIGS. 13 and 16 illustrate that the linear part34, constructed with two VCCS 34A and 34A′, or with two VCCS 34B and34B′, respectively, sources current from V_(bat) and sinks current toground. The operation is shown in the waveform diagrams of FIGS. 14 and15, and 17 and 18, respectively.

The circuit representations in FIGS. 13 and 16, and their correspondingwaveforms, illustrate the source/sink behavior of the VCVS 34A and theVCCS 34B, respectively, and model the behavior of the Power OperationalAmplifier and the Operational Transconductance Amplifier, respectively.Note that the two VCVS 34A in FIG. 13 are not active at the same time,and are preferably placed in a high impedance state when not active.

More specifically, FIGS. 13A and 13B illustrate this embodiment withideal sources, and the explanation given above for the circuit of FIG. 7applies here as well. A difference between the circuits is that in theembodiment of FIG. 13 the voltage sources VCVS 34A and 34A′ areuni-directional (one sources current, the other one sinks current),while in FIG. 7 the voltage source 34A is bi-directional (source andsink). The decoupling capacitor C_(d) may be included to ensure that thelinear part 34 contributes only the AC component.

With regard to the simulated waveform diagrams of FIGS. 14 and 15, asimilar explanation as was given above for FIGS. 8 and 9 also applies,except that the contribution of the linear part 34 i_(lin) ispartitioned into i_(aux1) (source) and i_(aux2) (sink). It should benoted again that the two voltage sources 34A and 34A′ (source and sink)are preferably placed in a high impedance state when their respectivecurrent is zero (i.e., when they are not active).

FIGS. 16A and 16B illustrate this embodiment of the invention with idealsources, and the explanation given above for the circuit of FIG. 10applies here as well. A difference between the circuits is that in theembodiment of FIG. 16 the current sources VCCS 34B and 34B′ areuni-directional (one sources current, the other one sinks current),while in FIG. 10 the current source 34B is bi-directional (source andsink). The decoupling capacitor C_(d) may be included to ensure that thelinear part 34 contributes only the AC component.

With regard to the simulated waveform diagrams of FIGS. 17 and 18, asimilar explanation as was given above for FIGS. I and 12 also applies,except that the contribution of the linear part 34 i_(lin) ispartitioned into i_(aux1) (source) and i_(aux2) (sink).

It is noted that FIGS. 7 and 10 are representations of interconnectionsof the power stages only (switching part 32 and linear part 34), withoutcontrol considerations. The switching part 32 is represented as a blockthat is controlled by control voltage V_(ctrl). The linear part 34 isrepresented as a block controlled by the differential voltage V_(d).FIGS. 21, 22 and 23 illustrate three non-limiting embodiments of controltechniques to close the control loops.

In FIG. 21 the switching part 32 operates with voltage-mode control. Thecontroller is composed of a control block 36A that generates an errorsignal V_(e1) and a block 36B with a frequency-dependent characteristicG_(e1)(s) that has as its input the error signal V_(e1) and as itsoutput the control voltage V_(ctrl) _(—) _(sw) for the switching part32. The error voltage V_(e1) is the difference between the referencevoltage V_(ref) _(—) _(sw), which is the modulating signal V_(m), andthe feedback signal V_(feedback) _(—) _(sw) which is the output voltageV_(pa). The controller (components 36A, 36B) in this case may bephysically implemented as an operational amplifier with an R-Ccompensation network to obtain the characteristic G_(c1)(s).

The linear part 34 uses the modulating signal V_(m) as the referenceV_(ref) _(—) _(lin). The feedback voltage V_(feedback) _(—) _(lin) isthe output voltage V_(pa). The feedback voltage V_(feedback) _(—) _(lin)may be taken as well before the decoupling capacitor C_(d) (if present),as shown with the dashed line. Similar to the switching part 32, thecontroller in this case is composed of a block 38A generating errorsignal V_(e2) and a block 38B with a frequency-dependent characteristicG_(c2)(S). As the linear part 34 is in fact preferably implemented witha Power Operational Amplifier, as in FIG. 19B, the control loop can beclosed around it by adding an R-C compensation network to obtain thecharacteristic G_(c2)(s), as one skilled in the art should realize. Notethat the VCVS 34A is included simply to show the voltage sourcecharacteristic of the linear stage 34, it is not the same VCVS shown inFIG. 7. The block labeled as “Linear part with feedback” is in fact arepresentation of the Power Operational Amplifier with the R-Ccompensation network.

Note that the same considerations as above apply for closing the loopwhen the linear stage 34 is constructed with the VCCS 34B (e.g., FIG.10) and the OTA shown in FIG. 20B.

In FIG. 22 the only significant difference versus FIG. 21 is that thereference signal of the switching part 32 is taken from the output ofthe linear part 34 (before the decoupling capacitor if present). Thesame considerations apply when the linear stage 34 uses the VCCS 34B andOTA. In this embodiment is clear that the linear part 34 has as itsreference the modulating signal V_(m), the AM signal, while theswitching part 32 has as its reference the output of the linear part 34(i.e., it is ‘slaved’ to the linear part 34).

In the embodiment of FIG. 23 the switching part 32 operates open-loop,meaning that only the modulating signal V_(m) is used to generate thePWM duty cycle d, and not the error signal V_(e1)=V_(m)−V_(pa). Thisexemplary embodiment may be particularly useful if stability problemsare potentially present with the two-loop control systems depicted inFIGS. 21 and 22. As before, the same considerations apply when thelinear stage 34 uses the VCCS 34B and the OTA.

The foregoing description of the embodiments of this invention provide asolution for achieving the fast modulation of the PA 6 power supply,where the fast modulation is provided primarily by the linear part 34,and uses the Buck converter with no or minimal filtering capacitance.However, it should be noted that the concept of connecting in parallel aswitching stage with a linear stage can be applied, and is useful, alsoin the case where a Buck converter is used in its conventional form,i.e., with a substantial output filtering capacitance C, and hence witha voltage source characteristic. For example, the RF transmitter for aGSM/EDGE case can be addressed with a fast switching converter, based ona Buck converter with voltage mode control. In this exemplary case thenecessary bandwidth can be achieved, however the dynamics are not ideal(i.e., the reference-to-output transfer function is not flat, butinstead may exhibit peaking) and thus the reference tracking is notoptimal. Moreover, the output voltage ripple due to the converterswitching action creates a spurious RF signal. Therefore, a linear stage34, connected in parallel with the Buck converter, can be used tocompensate for the non-ideal dynamics of the switching converter by“aiding” it and improving its tracking capability. In practice thelinear part 34 may also be used to improve (widen) the bandwidth, butits main role is to correct the reference-to-output characteristicalready provided by the switching part 32. Moreover, the linear part 34may compensate also for the output-voltage switching ripple (at least ina manner sufficient to meet the RF spurious requirements), by injectinga current to compensate for the inductor current ripple.

For the above reasons, it should be appreciated that the embodimentsgenerally represented by FIG. 5 may be extended to include circuitstructures where the switching part 32 is a “normal” Buck converter,i.e., where the output filter capacitance C is sufficiently large sothat the Buck converter behaves like a voltage source.

Based on the foregoing, it can be appreciated that the foregoingembodiments of this invention encompass circuit structures based on theBuck switched mode converter with no or but minimal filteringcapacitance C, i.e., where the output filter capacitance C is smallenough (or absent) so the Buck converter behaves substantially like acurrent source, where the linear part 34 alone is able to determine thebandwidth of the PA 6 supply, i.e. even with very slow switching part32, the linear part 34 is able to modulate due to the absence/minimalBuck converter filtering capacitor; where the linear part 34 providesalso the triangular AC component of the inductor current; and where thelinear part 34 compensates for the switching ripple.

Based on the foregoing, it can be appreciated that the foregoingembodiments of this invention also encompass circuit structures that arepreferably based on the Buck switched mode converter with significantfiltering capacitance C, i.e., where the output filter capacitance C issufficiently large so that the Buck converter behaves substantially likea voltage source. Thus, the embodiments of this invention also encompasscircuit structures based on a “normal” Buck converter circuit topologywith filtering capacitance; where the bandwidth is determined primarilyby the switching converter. In this case the linear part 34 may be usedto improve the bandwidth, but in a more limited way as the bandwidth isactually limited by the filtering capacitor C of the switchingregulator. An important role of the linear part 34 in these embodimentsis to aid and correct the dynamics of the switching part 32 (the Buckconverter). In this embodiment the linear part 34 may also compensatefor the switching ripple.

Aspects of this invention are based on the observation that the highfrequency components in, as examples, the EDGE and WCDMA envelope havevery low amplitude, while the majority of the energy is at DC and lowfrequencies. The low bandwidth switching part 32 processes the bulk ofthe power (DC and low frequency components) with high efficiency, whilethe wider bandwidth linear part 34 processes with lower efficiency onlya fraction of the power (the power corresponding to the high frequencycomponents). Therefore, it becomes possible to achieve the requiredbandwidth while still providing good efficiency. In general, theobtainable efficiency is less than would be achieved with a purelyswitching power supply, but still much greater than would be achievedwith a purely linear regulator-based power supply.

The principles of this invention apply without regard for the actualimplementation of the switching part 32 and/or the linear part 34, andcan be applied generally to transmitter architectures where the PA 6supply voltage needs to be modulated in amplitude. The teachings of thisinvention are not restricted to GSM/EDGE and WCDMA systems, but can beextended also to other systems (e.g. to CDMA systems). The teachings ofthis invention are not restricted to systems using a Class E PA 6, canbe applied also to systems using other types of saturated PAs.

Still further aspects of this invention, described in greater detailbelow, are directed to coupling to and supplying several PAs 6 in amulti-mode transmitter, as well as control for same methods.

Referring now to FIG. 24, there is shown an embodiment wherein aswitching regulator 100 and a linear regulator 102 are coupled inparallel to a SMPA 104 (e.g., a Class E PA) by means of an additionalinductor L₁ (i.e, additional to the conventional switching part 32inductor L shown in, for example, FIG. 7B) and an (optional) capacitorC₁. The PA 104 supply voltage V_(pa) is programmed with high accuracy bythe linear regulator 102. However, the instantaneous output voltage V₁of the switching regulator 100 cannot be accurately fixed at same valuedue to the low bandwidth, switching ripple and noise. Therefore, theadditional inductor L₁ is introduced to accommodate the instantaneousvoltage difference V_(pa)−V₁. The average voltage over L₁ must be zero,hence the average of V₁ equals V_(pa).

If the decoupling capacitor C₁ is present, the linear regulator 102 canprovide only AC components in a certain range of frequencies, whichpreferably complement the lower bandwidth of the switching regulator 100to obtain the desired overall bandwidth.

If C₁ is not present, the linear regulator 102 can also provide DC andlow frequency components. This may be particularly advantageous undercertain conditions, for example when the PA 104 voltage V_(pa) should beas close as possible to the battery voltage V_(bat). One such situationis in the GSM case, at maximum RF output power (the PA 104 needs minimumvoltage, e.g., 2.7V), with low battery voltage (e.g., 2.9V). In thiscase the difference between the input voltage and the output voltage ofany regulator interposed between the battery and the PA 104 is very low(only 0.2V in this example). This is a very difficult value to obtainwith the switching regulator 100 (considering the voltage drop on onepower device, plus the two inductors L and L₁, at a duty cycle<100%). Inthis particular case, the linear regulator 102 can be used to providethe supply voltage nearer to the battery voltage, and thus the linearregulator 102 provides all of the power (DC component, and no capacitorC₁). While in this particular case (GSM, max output power, low batteryvoltage) the efficiency would not be affected because the voltage dropon the linear regulator 102 is small, at lower GSM power levels (i.e.larger drop on the linear regulator 102) the efficiency would bedegraded. Therefore, at lower power levels it is more advantageous touse the switching regulator 100 to provide all of the power (DCcomponent).

In FIG. 24 the supply voltage for the linear regulator 102 is V_(bat),the same as for the switching regulator 100. While this may be optimumfrom an implementation point of view, it may not be optimal from anefficiency point of view. At lower power levels, where V_(m) _(—) _(pk)is much lower than V_(bat), the voltage drop on the linear regulator 102is large and its efficiency is poor. Therefore, a more efficienttechnique pre-regulates (with high efficiency) the supply voltage of thelinear regulator 102 at some level, e.g., 200–300 mV above the peakvalue of the envelope V_(m) _(—) _(pk) (see FIG. 2).

As seen from FIGS. 3 and 4, each of the two building blocks (switchingand linear) of the hybrid regulator has its own control loop. Theoverall control must be made in such a way that the two blockscomplement each other. Two possible control schemes are shown in FIG.25.

In FIG. 25A both regulators 100, 102 are ‘master’, as each has themodulating signal V_(m) as a reference and each regulator 100, 102receives its feedback signal (V_(feedback) _(—) _(sw), V_(feedback) _(—)_(in)) from its own output.

In FIG. 25B the linear regulator 102 is the ‘master’, i.e. it has as areference signal the modulating signal V_(m) and its own output as thefeedback signal. The switching regulator 100 is a ‘slave’, meaning thatit has as a reference signal the voltage applied to the SMPA 104 by thelinear regulator 102, and attempts to follow it as accurately aspossible.

These embodiments of this invention are particularly well suited forapplication in a multi-mode transmitter, as explained below.

As a first non-limiting example, in GSM the RF envelope is constant, sothe voltage supplied to the PA 104 is constant and its level is adjustedaccording to the desired power level. The main function of the SMPA 104power supply in this case is power control. In principle using only theswitching regulator 100 would be sufficient. However, the switchingaction generates output voltage ripple and noise, which are seen asspurious signals in the RF spectrum at SMPA 104 output. In this mode thelinear regulator 102 may be employed, if needed, to compensate for theoutput voltage ripple of the switching regulator 100. By doing so, it isalso possible to relax the specification of the output voltage ripplefor the switching regulator 100. For example, if one assumed a typicalvoltage ripple specification of 5 mV for the switching regulator 100,with ripple compensation supplied by the linear regulator 102 thespecification may possibly be relaxed to 50 mV, allowing for smaller LCcomponents in the switching regulator 100 and/or faster dynamics of theswitching regulator 100. In this case the switching regulator 100processes almost all of the required SMPA power, while the linearregulator 102 processes very little (only that needed for ripplecompensation).

In the EDGE system or, in general, any system having a variable RFenvelope with moderately high dynamics (e.g., required BW>1 MHz), themain functions of the SMPA 104 power supply are power control andenvelope tracking. It can be shown that a purely switching regulatorwith a 6–7 MHz switching frequency is capable of tracking withrelatively good accuracy the EDGE RF envelope. However, the system isnot robust when using a purely switching regulator, and may exhibitsensitivity to, for example, peaking in the reference-to-output transferfunction of the switching regulator 100, and to variations of the SMPA104 load with the supply voltage (generally the resistance of the SMPAincreases as the supply voltage decreases). In addition, there is alsothe problem of the output voltage ripple, as discussed above. Inaccordance with this aspect of the invention the linear regulator 102can be used, if needed, to compensate for the non-optimal dynamics ofthe switching regulator 100, the SMPA 104 load variation and theswitching ripple. If the switching frequency of the switching regulator100 is sufficiently high enough to allow for good tracking capability,most of the power is processed by the switching regulator 100. However,it is also possible to use a switching regulator 100 with a lowerswitching frequency, hence with a lower bandwidth, in which case theproportion of the power processed by the linear regulator 102 increasesto compensate for the reduction by the switching regulator 100.

In the WCDMA system or, in general, any system that exhibits a variableRF envelope with high dynamics (e.g., a required BW>15 MHz) the mainfunctions of the SMPA 104 power supply are both power control andenvelope tracking. However, since the required bandwidth is much higherthat for the EDGE system, the use of only the switching regulator 100(in CMOS technology) is not adequate, and the use of the linearregulator 102 becomes important to provide the required bandwidth. As inthe EDGE case, the linear regulator 102 can also compensate for theswitching ripple and the SMPA 104 load variation.

A further utility gained from the use of embodiments of this inventionis an ability to provide multi-mode operation with a plurality of PAs.One non-limiting example is the Class E GSM/EDGE PA 104A and the Class EWCDMA PA 104B shown in FIG. 26. In this case all of the PAs 104A, 104Bare connected on same supply line at the output of the linear regulator102. This embodiment assumes, as do the embodiments of FIGS. 27, 29 and30, that there is a mechanism present (e.g., a switch) to enable onlyone PA 104A or 104B at a time.

Note that the PAs 104A and 104B are not limited to being Class E PAs, asthese are shown for convenience only. The same is true for theembodiments shown in FIGS. 27, 29 and 30.

In FIG. 26A both regulators 100, 102 can be viewed as ‘masters’, i.e.,both have as their reference the modulating signal V_(m) and both havetheir own respective output voltages to provide their feedbackinformation. In FIG. 26B the linear regulator 102 is the ‘master’ andthe switching regulator 100 is the ‘slave’, meaning that its referencesignal is the output of the linear regulator, V_(pa).

FIG. 27 shows additional multi-mode configurations, where the GSM/EDGEPA 104A is connected at the output of the switching regulator 100(between the output and L₁) and the WCDMA PA 104B is connected at theoutput of the linear regulator 102. This configuration is useful for, aswas noted previously, in GSM/EDGE the required performance may beachieved with the purely switching regulator 100. With this assumption,in GSM/EDGE one uses only the switching regulator 100 and disables thelinear regulator 102. This has a positive impact on efficiency, becauselosses introduced by inductor L₁ are eliminated. It also permits one toobtain a maximum GSM/EDGE PA supply voltage V₁ that is nearer to thebattery voltage V_(bat), as the voltage drop on L₁ is eliminated. Theinductor L₁ can be smaller, as it has to handle only the lesser PA 104Bcurrent in the WCDMA mode of operation. In this embodiment the linearregulator 102 is enabled only in the WCDMA mode.

Note that if all of the PAs 104A and 104B are connected to the samesupply line, as was shown in FIG. 26, the total decoupling capacitancemay be too large. The PA 104 (a Class E PA as a non-limiting example)can be modeled, in a first approximation and from a regulator point ofview, by its equivalent DC resistance R_(pa), as shown in FIG. 28. Inpractice, and for PA stability reasons, it is typically necessary toconnect at least one decoupling capacitor C_(pa) in parallel with the PA104. If there are several PAs 104 connected on same supply line, it maybe possible to use one or more common (shared) decoupling capacitors. Inthat case, the connection shown in FIG. 26 is possible. However, if eachPA 104 must have its own decoupling capacitors, e.g., because thecapacitors must be placed within a PA module, then the total decouplingcapacitance may become excessive, making it impossible to achieve thewide bandwidth needed in, for example, the WCDMA mode of operation.

One solution to this problem is use switches to disconnect from thesupply line the inactive PA(s), or at least their decoupling capacitors.Another possible solution is to connect the PAs 104A, 104B onindependent supply lines, for example as shown in FIG. 27.

In FIG. 27A both regulators 104A, 104B are connected as ‘masters’. InGSM/EDGE, and assuming that acceptable performance can be obtained, thelinear regulator 102 may be disabled and only the switching regulator100 is used. However, it may be possible to also use the linearregulator 102, by-passing L₁, for (some) ripple compensation and dynamicperformance improvement. If this case the linear regulator 102 isenabled as well, and its feedback information is V₁ applied throughSwitch 1 (SW1) in the GSM/EDGE position. In the WCDMA mode bothregulators 100, 102 are enabled and the feedback information for thelinear regulator is V_(pa) (SW1 is in the WCDMA position).

In the embodiment shown in FIG. 27B the switching regulator 100 isconnected as a ‘slave’ for the WCDMA case (both SW1 and SW2 are in theWCDMA position), and receives its V_(ref-sw) signal via SW2 from theoutput of the linear regulator 102. In the GSM/EDGE mode (both SW1 andSW2 are in the GSM/EDGE position) the configuration and operatingconsiderations are as described above for FIG. 27A.

FIG. 29 shows additional multi-mode configurations, where the PAs 104A,104B are connected to independent supply lines at the output ofindividual linear regulators 102A, 102B. This configuration is anextension of the multi-mode configuration shown in FIG. 26. There isonly one switching regulator 100, and the PAs 104A, 104B are connectedon individual supply lines each assisted by an associated linearregulator 102A, 102B, respectively, and isolated via associatedinductors L₁ and L₂, respectively. This configuration aids in overcomingthe problem of excessive decoupling capacitance C_(pa) described earlierwith respect to FIG. 28.

In FIG. 29A the switching regulator 100 and both linear regulators 102A,102B are connected as ‘masters’, while in FIG. 29B the switchingregulator 100 is connected as a ‘slave’, where its reference voltage isthe output of the linear regulator 102A or 102B as selected by S1according to the currently active system (GSM/EDGE or WCDMA).

FIG. 30 shows additional multi-mode configurations, where the GSM/EDGEPA 104A is connected at the output of the switching regulator 100(between the output and L₁), and where the WCDMA PA 104B and a CDMA PA104C are connected on independent supply lines at the output ofindividual linear regulators 102A, 102B, respectively. This embodimentmay be considered as an extension of the multi-mode embodiments shown inFIGS. 27 and 29. This embodiment is particularly useful if the GSM/EDGEPA 104A can be connected directly to the output of the switchingregulator 100, and if there are at least two other PAs that require fastsupply voltage modulation and that can be placed on independent supplylines.

In FIG. 30A the switching regulator 100 and both linear regulators 102A,102B are connected as ‘masters’, while in FIG. 30B the switchingregulator 100 is connected as a ‘slave’ in only the WCDMA and CDMA modesof operation, where its reference voltage is the output of the linearregulator 102A or 102B as selected by the three pole switch S1 accordingto the currently active system (WCDMA or CDMA). In the GSM/EDGE mode theswitching regulator 100 receives its V_(ref) _(—) _(sw) input, via S1,from the V_(m) input, and thus functions as in FIG. 30A.

It should be appreciated that FIG. 21 shows a configuration where boththe switching part 32 and the linear part 34 are ‘masters’, FIG. 22shows a configuration where the linear part 34 is the ‘master’ and theswitching part 32 is the ‘slave’, and FIG. 23 shows a configurationwhere both the switching part 32 and the linear part 34 are ‘masters’,and the switching part 32 operates open loop. In a further embodiment ofthis invention the switching part 32 may function as the ‘master’ andthe linear part 34 as the ‘slave’.

As the switching part 32 is relatively slow, it is preferred not too useits output V_(pa) as the reference signal to ‘slave’ the linear part.With reference to FIG. 21, the signal V_(ctrl) _(—) _(sw) is in directrelationship with d, the duty-cycle of the PWM voltage applied to the LCfilter at the pulse width modulator 32 node. In the steady state(constant V_(ref) _(—) _(sw)), V_(ctrl) is proportional with the outputvoltage V_(pa). The situation is different, however, in the dynamicstate (varying V_(ref) _(—) _(sw)). If, for example, a fast increase inV_(pa) is commanded through V_(ref) _(—) _(sw), the effect is a rapidincrease in the error signal V_(e1), a resulting rapid increase inV_(ctrl) _(—) _(sw), which at its turn commands an increase of theduty-cycle d. As a consequence of the increased duty-cycle, V_(pa)eventually increases (slowly) to a new, higher level. Due to the LCfilter, the response of the switching converter in increasing V_(pa) ismuch slower than the response in increasing V_(ctrl) _(—) _(sw) and therelated duty-cycle d. In other words, V_(ctrl) _(—) _(sw) containsinformation of what is to occur with the output voltage V_(pa). Anincrease in V_(ctrl) _(—) _(sw) implies an increase in the duty-cycle d,hence it means that the output voltage V_(pa) must increase. Thisinformation may be used to signal the linear part 34 to source currentin order to aid in increasing V_(pa). Relatedly, a decrease in V_(ctrl)_(—) _(sw) implies a decrease in the duty-cycle d, and hence it meansthat the output voltage V_(pa) must decrease. This can be used to signalthe linear part 34 to sink current to aid in decreasing V_(pa). Thus,V_(ctrl) _(—) _(sw) contains valuable information, which can be used to‘slave’ the linear stage 34.

With reference to the foregoing, this aspect of the invention providesyet another control mechanism wherein, as in FIG. 21, instead of V_(ref)_(—) _(lin)=V_(m), there is instead the relationship V_(ref) _(—)_(lin)=G_(c3)*V_(ctrl) _(—) _(sw), where G_(c3)(s) represents in asimplest case some amount of voltage scaling, and in a more complex casehas also a frequency dependent characteristic. Assume as a non-limitingexample that G_(c3)(s)=1. As mentioned above, in the steady-state(constant V_(ref) _(—) _(sw)), V_(ctrl) _(—) _(sw) is proportional tothe output voltage V_(pa). Assume further for this non-limiting examplethat the proportionality constant is unity, so that V_(pa)=V_(ctrl) _(—)_(sw), and thus also that V_(ref) _(—) _(lin)=V_(ctrl) _(—) _(sw), sothat V_(pa)=V_(ref) _(—) _(lin)→V_(e2)=0→ no contribution from thelinear part 34. If a fast increase in V_(ref) _(—) _(sw) is provided,this results in a fast increase in V_(ctrl) _(—) _(sw), as explainedabove, and thus also a fast increase in V_(e2) results in a command tothe linear part 34 to source additional current. Similarly, if a fastdecrease in V_(ref) _(—) _(sw) is provided, this results in a fastdecrease in V_(ctrl) _(—) _(sw) resulting in a fast decrease in V_(e2),and the linear part 34 is thus commanded to sink current. Thus, in thismanner the linear part 34 is essentially ‘slaved’ to the switching part32.

Similar considerations apply in relation to the embodiment of FIG. 23,where the switching part 32 operates open loop, and also to theembodiments of FIG. 25A and the related FIGS. 26, 27, 29 and 30. Inspecific relation to FIG. 25A, the control configuration described aboveimplies that, instead of V_(ref) _(—) _(lin)=V_(m), we have therelationship V_(ref) _(—) _(lin)=V_(ctrl) _(—) _(sw). Note that whileV_(ctrl) _(—) _(sw) is not shown in FIG. 25, V_(ctrl) _(—) _(sw) isassumed to be an internal signal to the switching regulator 100 block,which has the structure shown in, for example, FIG. 21, i.e., theswitching part 32 in addition to the controls 36A and 36B.

It should be appreciated that these various embodiments of the inventionallow the realization of an efficient PA power supply for a multi-modetransmitter architecture wherein the PA supply voltage maybe amplitudemodulated. Some advantages of the use of these embodiments includeimproved efficiency that leads to longer talk time and improved thermalmanagement, and/or an ability to achieve a required bandwidth, and/or anability to implement a multi-mode transmitter with one device (the priorassumption being that at least the GSM/EDGE and WCDMA cases should beprovided with separate devices).

The use of the embodiments of this invention provides a number ofadvantages, including high power conversion efficiency. Relatedly, inbattery-powered communications devices a longer talk time is provided.Thermal management issues are also more effectively managed, as comparedto the use of the purely linear DC-DC converter, and there is also thepotential to eliminate altogether, or a least reduce the size of, atleast one power supply filtering capacitor (e.g., the capacitor C inFIG. 4A).

It is pointed out the conversion made in the switching part 32 orswitching regulator 100 is described as step-down, and with voltage modecontrol, which is the presently preferred embodiment. However, it shouldbe realized that the conversion could be step-up/step-down. Step-up/downis beneficial but it is more difficult to implement. Step-up/downenables lowering the cut-off voltage in the mobile station, such as acellular telephone, as the battery voltage decreases as its charge isdepleted, and the cut-off voltage is the minimum voltage for the mobilestation to be operational. With too low a voltage the PA 6 is not ableto produce full output power, and step-up/down solves this problem. Forexample, by the use of a step-up/down switching part 32 one mayaccommodate a V_(bat) lower than V_(m) _(—) _(pk) (FIG. 2), whereas withonly step-down V_(bat) must be at least equal to V_(m) _(—) _(pk) plussome margin, e.g. V_(m) _(—) _(pk)+0.2V. With fast AM modulation asshown in FIG. 2, the transition is controlled between the step-up andstep-down characteristic in such a way that this transition does notcause distortion of the output voltage V_(pa). Further, with astep-up/down switching part or converter, and when V_(m) _(—)_(pk)>V_(bat), the linear part 34 must be supplied from a DC sourcewhich is greater than V_(m) _(—) _(pk) and, hence, greater than V_(bat)in order to be able to source current.

It can further be noted that in voltage mode control only voltageinformation (e.g. the output voltage of the converter) is used togenerate the control signal. However, it is also possible to use alsocurrent mode control where, in addition to the voltage, currentinformation is also used (e.g., the inductor current). In current modecontrol there are two control loops, one for current and one forvoltage. Of course, other, more complex, types of controls may also beused.

In view of the foregoing description of the preferred embodiments ofthis invention, it should be realized that these teachings are notrestricted for use with only GSM/EDGE, WCDMA and/or CDMA systems, butcan be used to advantage in any type of system having a varyingamplitude envelope, where the PA supply voltage should be modulated withhigh efficiency and high bandwidth.

In view of the foregoing description of the preferred embodiments ofthis invention, it should be realized that these teachings are notrestricted for use with only Class E PAs, but in general can be appliedto a number of SMPAs as well as normally linear PAs operated insaturation, such as the saturated Class B PA.

In view of the foregoing description of the preferred embodiments ofthis invention, it should be realized that these teachings are notrestricted for use with any specific type of switching convertertopology (e.g., not only Buck, not only step-down, but alsostep-up/down), and not with only voltage mode control.

In view of the foregoing description of the preferred embodiments ofthis invention, it should be realized that these teachings are notrestricted for use with only a switching part that provides DC and alinear part that provides AC. In practice, it is desired that theswitching part provides AC also, as much as possible (as it tries tofollow the reference), and that the linear part provides the missingpart of the AC (or the missing bandwidth). In this manner theembodiments of this invention enhance as much as possible the overallefficiency, as in principle the greater is the contribution from theswitching part or converter, the greater is the efficiency.

In view of the foregoing description of the preferred embodiments ofthis invention, it should be realized that while the linear stage(s)compensate for the non-ideal dynamics of the switching stage, non-idealdynamics are also partly caused by non-ideal PA behavior (e.g. loadvariations), in the sense that R_(pa) changes with V_(pa) (i.e.,increases when V_(pa) decreases) and in mismatch conditions. Thus, thelinear stage(s) 34, 102 compensate at least for non-ideal dynamics ofthe switching converter (e.g., insufficient bandwidth and/or peaking inthe reference-to-output characteristic). Further in this regard thelinear stage(s) 34, 102 and the switching stage 32, 100 complement eachother to obtain a specific desired reference-to-output transfer function(not only a specific bandwidth, but also a specific shape of thetransfer function). For example, the linear stages 34, 102 may have sucha reference-to-output transfer function that the resultingreference-to-output transfer function of the hybrid (switching/linear)power supply is or approximates a flat 2^(nd) order Butterworth filtertype. Thus, the linear stage(s) 34, 102 can be used to shape theresulting overall reference-to-output transfer function in order toobtain the desired characteristic. The linear stage(s) 34, 102 also aidin tracking the reference signal, and can be used to obtain a specificdesired tracking capability of the reference signal V_(m).

The linear stage(s) 34, 102 may also compensate at least for switchingripple, and may also compensate at least for non-ideal PA behavior, suchas R_(pa) variation with operating conditions.

It should be further understood that the auxiliary inductor L₁introduced in FIG. 24 has, in practice, a similar role as the converterinductor L shown in FIG. 6 in that its effect is to create a currentsource characteristic. One distinction is that in the embodiments ofFIG. 6, and those following, a PWM rectangular voltage is applied at theinput of the inductor L, while in the embodiment of FIG. 24, and thosefollowing, an already smoothed voltage (the output of the switchingconverter 100) is applied to the input of the auxiliary inductor L₁.

In view of the foregoing description of the preferred embodiments ofthis invention, it should also be realized that in the GSM/GMSKmodulation case the hybrid power supply performs a “power control”function, whereby the power level is adjusted by adjusting the voltagelevel with the power supply. As such, it can be appreciated that asopposed to AM control, what is used instead is “step control”. Note thata goal may be to improve the PA 6 efficiency, particularly when using alinear PA. With the linear PA typically there will exist anothermechanism to adjust the power level, even with constant supply voltageV_(bat), but then the efficiency decreases at lower power levels and theDC level can be lowered to improve the efficiency. With the SMPA,however, the output power is controlled (mainly) by the supply voltage.As such, it is desirable to use the PA power supply 30 to control thepower.

In any event, for the fast hybrid power supply 30 in accordance with thepreferred embodiments of this invention, and for the GSM case: a) in theTX architecture the PA power supply is used to control the power; b) thePA power supply does not have to be very fast (while there are somerequirements related to power ramp-up/down, they are less demanding thanthe EDGE case); and c) it is beneficial to compensate the switchingripple with the hybrid power supply 30, just as in the EDGE case.

The foregoing description has provided by way of exemplary andnon-limiting examples a full and informative description of the bestmethod and apparatus presently contemplated by the inventor for carryingout the invention. However, various modifications and adaptations maybecome apparent to those skilled in the relevant arts in view of theforegoing description, when read in conjunction with the accompanyingdrawings and the appended claims. For example, while the power supply ofthis invention has been described above in the context of a polar or ERtransmitter embodiment, the invention can be applied other applicationswherein a power supply must meet stringent dynamic requirements, whilealso exhibiting high efficiency. Further, the various embodiments ofFIGS. 6–30 are not to be construed in a limiting sense upon the numberof possible embodiments that the hybrid voltage regulator may assume, orof the types of RF power amplifiers and RF communication systems thatthe embodiments of this invention can be used with. In general, all suchand similar modifications of the teachings of this invention will stillfall within the scope of the embodiments of this invention.

Further still, some of the features of the present invention could beused to advantage without the corresponding use of other features. Assuch, the foregoing description should be considered as merelyillustrative of the principles of the present invention, and not inlimitation thereof.

1. A radio frequency (RF) transmitter (TX) for coupling to an antenna,said TX having a polar architecture comprised of an amplitude modulation(AM) path coupled to a power supply of a power amplifier (PA) and aphase modulation (PM) path coupled to an input of the PA, where saidpower supply comprises a switch mode part for coupling between a powersource and the PA, the switch mode part providing x amount of outputpower, said power supply further comprising a linear mode part coupledin parallel with the switch mode part between the power source and thePA, the linear mode part providing y amount of output power, where x isgreater than y, and the ratio of x to y is optimized for particularapplication constraints, and where the linear mode part exhibits afaster response time to a required change in output voltage than theswitch mode part.
 2. A RF TX as in claim 1, where the linear mode partcomprises at least one power operational amplifier operating as avariable voltage source.
 3. A RF TX as in claim 1, where the linear modepart comprises at least one power operational transconductance amplifieroperating as a variable current source.
 4. A RF TX as in claim 1, wherethe linear mode part provides only an AC component to the PA.
 5. A RF TXas in claim 1, where the linear mode part provides a DC component and anAC component to the PA.
 6. A RF TX as in claim 1, where the output ofthe linear mode part compensates for AC ripple output from the switchmode part.
 7. A RF TX as in claim 1, where the linear mode partcomprises a bi-directional voltage controlled voltage source.
 8. A RF TXas in claim 1, where the linear mode part comprises a bi-directionalvoltage controlled voltage source (VCVS), and comprises two VCVScircuits, where in operation one operates as a sink and one as a source.9. A RF TX as in claim 1, where the linear mode part comprises abi-directional voltage controlled current source.
 10. A RF TX as inclaim 1, where the linear mode part comprises a bi-directional voltagecontrolled current source (VCCS), and comprises two VCCS circuits, whereone operates as a sink and one as a source.
 11. A RF TX as in claim 1,where the switch mode part and the linear mode part are controlled incommon by a control signal in a closed-loop manner, where the controlsignal comprises an AM signal.
 12. A RF TX as in claim 1, where theswitch mode part is controlled by an output from the linear mode part ina closed-loop manner, and where the linear mode part is controlled by acontrol signal in a closed-loop manner, where the control signalcomprises an AM signal.
 13. A RF TX as in claim 1, where the switch modepart is operated open-loop, and where the linear mode part is controlledby a control signal in a closed-loop manner, where the control signalcomprises an AM signal.
 14. A RF TX as in claim 1, where the linear modepart is effectively slaved to operation of the switch mode part tosource or sink current.
 15. A RF TX as in claim 1, where the switch modepart is provided with minimal or no output filter capacitance tofunction substantially as a current source.
 16. A RF TX as in claim 1,where the switch mode part is provided with an output filter capacitanceand functions substantially as a voltage source.
 17. A RF TX as in claim1, where the switch mode part is coupled to the PA and to the output ofthe linear mode part through an inductance.
 18. A RF TX as in claim 1,where the switch mode part is coupled to the PA and to the output of thelinear mode part through an inductance, and where the linear mode partis coupled to the output of the switch mode part, via the inductance,and to the PA through a capacitance.
 19. A RF TX as in claim 1, wheresaid power supply provides a greater power conversion efficiency than apurely linear voltage regulator-based power supply while also providinga wider operational bandwidth than a purely switch mode-based powersupply.
 20. A RF TX as in claim 1, where the linear mode part is coupledto the output of the switch mode part and to the load through acapacitance.
 21. A RF TX as in claim 1, where the linear mode partcompensates at least in part for variations in the load presented by thePA.
 22. A RF TX as in claim 1, where the linear mode part compensates atleast in part for non-ideal dynamics of the switch mode part.
 23. Aradio frequency (RF) transmitter (TX) for coupling to an antenna, saidTX having a polar architecture comprised of an amplitude modulation (AM)path coupled to a power supply of a power amplifier (PA) and a phasemodulation (PM) path coupled to an input of the PA, where said powersupply comprises a switch mode stage for coupling between a power sourceand the PA, the switch mode stage providing x amount of output power,said power supply further comprising at least one linear mode stagecoupled in parallel with the switch mode stage between the power sourceand the PA, the linear mode stage providing y amount of output power,where x is greater than y, and the ratio of x to y is optimized forparticular application constraints, further comprising at least oneauxiliary inductance coupled between an output of the switch mode stageand an output of the at least one linear mode stage.
 24. A RF TX as inclaim 23, where the PA is coupled to the output of the switch mode stagebefore the auxiliary inductance, and further comprising at least oneadditional PA coupled to the output of the switch mode stage after theauxiliary inductance.
 25. A RF TX as in claim 23, where the PA iscoupled to the output of the switch mode stage after the auxiliaryinductance, and further comprising at least one additional PA alsocoupled to the output of the switch mode stage after the auxiliaryinductance.
 26. A RF TX as in claim 23, where the PA is coupled to theoutput of the switch mode stage before a first auxiliary inductance anda second auxiliary inductance, and further comprising a second PAcoupled to the output of the switch mode stage after the first auxiliaryinductance, and a third PA coupled to the output of the switch modestage after the second auxiliary inductance.
 27. A RF TX as in claim 26,where the second PA is further coupled to the output of a first linearpower stage, and the third PA is coupled to the output of a secondlinear power stage.
 28. A RF TX as in claim 23, where the PA is coupledto the output of the switch mode stage after a first auxiliaryinductance, and further comprising a second PA coupled to the output ofthe switch mode stage after a second auxiliary inductance, where the PAis further coupled to the output of a first linear power stage, and thesecond PA is coupled to the output of a second linear power stage.
 29. ARF TX as in claim 23, where the at least one linear mode stage comprisesat least one power operational amplifier operating as a variable voltagesource.
 30. A RF TX as in claim 23, where the at least one linear modestage comprises at least one power operational transconductanceamplifier operating as a variable current source.
 31. A RF TX as inclaim 23, where the at least one linear mode stage provides only an ACcomponent to the PA.
 32. A RF TX as in claim 23, where the at least onelinear mode stage provides a DC component and an AC component to the PA.33. A RF TX as in claim 23, where the output of the at least one linearmode stage compensates for AC ripple output from the switch mode stage.34. A RF TX as in claim 23, where the switch mode stage and the at leastone linear mode stage are controlled in common by a control signal in aclosed-loop manner, where the control signal comprises an AM signal. 35.A RF TX as in claim 23, where the switch mode stage is controlled by anoutput from the at least one linear mode stage in a closed-loop manner,and where the at least one linear mode stage is controlled by a controlsignal in a closed-loop manner, where the control signal comprises an AMsignal.
 36. A RF TX as in claim 23, where the switch mode stage isoperated open-loop, and where the at least one linear mode stage iscontrolled by a control signal in a closed-loop manner, where thecontrol signal comprises an AM signal.
 37. A RF TX as in claim 23, wherethe at least one linear mode stage is effectively slaved to operation ofthe switch mode stage to source or sink current.
 38. A RF TX as in claim23, where the switch mode stage is provided with an output filtercapacitance and functions substantially as a voltage source, andprovides a smoothed voltage signal to said auxiliary inductance.
 39. ARF TX as in claim 23, where the at least one linear mode stage iscoupled to the output of the switch mode stage and to the PA through acapacitance.
 40. A BY TX as in claim 23, where the at least one linearmode stage compensates at least in part for variations in the loadpresented by the PA.
 41. A RF TX as in claim 23, where the at least onelinear mode stage compensates at least in part for non-ideal dynamics ofthe switch mode stage.
 42. A RF TX as in claim 23, further comprising aswitch coupled to a reference input of said switch mode stage forselectively applying different reference signals to said switch modestage as a function of a mode of operation.
 43. A RF TX as in claim 42,where one mode of operation comprises a GSM mode.
 44. A RF TX as inclaim 42, where one mode of operation comprises an EDGE mode.
 45. A RFTX as in claim 42, where one mode of operation comprises a CDMA mode.46. A RF TX as in claim 42, where one mode of operation comprises aWCDMA mode.
 47. A RF TX as in claim 23, further comprising a switchcoupled to a feedback input of said at least one linear mode stage forselectively applying different feedback signals to said at least onelinear mode stage as a function of a mode of operation.
 48. A RF TX asin claim 47, where one mode of operation comprises a GSM mode.
 49. A RFTX as in claim 47, where one mode of operation comprises an EDGE mode.50. A RF TX as in claim 47, where one mode of operation comprises a CDMAmode.
 51. A RF TX as in claim 47, where one mode of operation comprisesa WCDMA mode.
 52. A method to operate a radio frequency (RF) transmitter(TX), where the TX has a polar architecture comprised of an amplitudemodulation (AM) path coupled to a power supply of a power amplifier (PA)and a phase modulation (PM) path coupled to an input of the PA,comprising: providing the power supply so as to comprise a switch modepart for coupling between a power source and the PA, the switch modepart providing x amount of output power; and coupling a linear mode partin parallel with the switch mode part between the power source and thePA, the linear mode part providing y amount of output power, where x isgreater than y, and the ratio of x to y is optimized for particularapplication constraints, and where the linear mode part exhibits afaster response time to a required change in output voltage than theswitch mode part.
 53. A method as in claim 52, where the linear modepart comprises at least one power operational amplifier operating as oneof a variable voltage source or at least one power operationaltransconductance amplifier operating as a variable current source.
 54. Amethod as in claim 52, where the linear mode part provides only an ACcomponent to the PA.
 55. A method as in claim 52, where the linear modepart provides a DC component and an AC component to the PA.
 56. A methodas in claim 52, further comprising operating the linear mode part tocompensate for at least one of AC ripple output from the switch modepart, variation in the load presented by the PA, and non-ideal dynamicsof the switch mode part.
 57. A method as in claim 52, where the linearmode part comprises one of a bi-directional voltage controlled voltagesource and a bi-directional voltage controlled current source.
 58. Amethod as in claim 52, further comprising controlling in common theswitch mode part and the linear mode part with a control signal in aclosed-loop manner, where the control signal comprises an AM signal. 59.A method as in claim 52, further comprising controlling the switch modepart with an output from the linear mode part in a closed-loop manner,and controlling the linear mode part in a closed-loop manner with acontrol signal that comprises an AM signal.
 60. A method as in claim 52,further comprising operating the switch mode part in an open-loopmanner, and controlling the linear mode part in a closed-loop mannerwith a control signal that comprises an AM signal.
 61. A method as inclaim 52, further comprising operating the linear mode part so as to beeffectively slaved to operation of the switch mode part to source orsink current.
 62. A method as in claim 52, comprising operating theswitch mode part to function substantially as a current source.
 63. Amethod as in claim 52, comprising operating the switch mode part tofunction substantially as a voltage source.
 64. A method as in claim 52,further comprising coupling the switch mode part to the PA and to theoutput of the linear mode part through an inductance.
 65. A method as inclaim 52, further comprising coupling the switch mode part to the PA andto the output of the linear mode part through an inductance, and wherethe linear mode part is coupled to the output of the switch mode part,via the inductance, and to the PA through a capacitance.
 66. A method asin claim 52, further comprising coupling the linear mode part to theoutput of the switch mode part and to the PA through a capacitance.